Method and apparatus for optical disk recording capable of reducing settling time and generating an accurate channel clock signal

ABSTRACT

An optical disk recording apparatus includes a first comparator, a second comparator, a third comparator, a selection circuit, a control voltage generator, a voltage control oscillator, and a control circuit. The first comparator compares frequency-divided signals to output an error signal. The second and third comparators compare a signal pre-recorded on an optical disk and the frequency-divided signal to output an error signal and a frequency differential signal. The selection circuit selects any one of the error signals to output the signal selected. The control voltage generator generates a control voltage from the signal from the selection circuit. The voltage control oscillator generates and outputs the write reference clock signal having a frequency corresponding to the control voltage from the control voltage generator. The control circuit controls operations of the selection circuit according to the frequency differential signals.

BACKGROUND

[0001] 1. Field

[0002] This application generally relates to an optical recordingapparatus for recording data on optical disks such as a CD-R/RW, aDVD+R/RW, a DVD−R/RW, and, in particular, to an optical recordingapparatus which employs a constant angular velocity (CAV) recordingmethod.

[0003] 2. Discussion of the Background

[0004] In conventional optical disk recording apparatuses, a constantlinear velocity (CLV) method has been employed for recording informationon optical disks. In the CLV method where a channel clock signal used asa reference for recording/reproducing is constant regardless of aposition in a radius of a disk, a channel clock signal is generated froma constant reference clock signal from outside generated by using acrystal or the like. In these days, however, in order to increase arecording speed and to reduce power consumption in recording ontooptical disks, a constant angular velocity (CAV) recording method hasbeen employed for DVD recording standards. For example, Japanese PatentLaid-Open Application Publications, No. 2001-6297 and No. 2000-173195,describe optical disk apparatuses employing the CAV method for readingout data from optical disks.

SUMMARY

[0005] This application describes a novel optical disk recordingapparatus that records information on a recordable optical diskemploying a constant angular velocity recording method and generates awrite reference clock signal used for obtaining recording timing in adata-recording operation on the optical disk. In one example, a noveloptical disk recording apparatus includes a first comparator, a secondcomparator, a third comparator, a selection circuit, a control voltagegenerator, a voltage control oscillator, and a control circuit. Thefirst comparator is configured to compare phases and frequencies betweena frequency-divided signal of a predetermined reference clock signalinput from outside and a frequency-divided signal of the write referenceclock signal, and to output a first error signal representing comparisonresults. The second comparator is configured to compare phases andfrequencies between a first signal recorded beforehand on the opticaldisk and the frequency-divided signal of the write reference clocksignal, and to output a second error signal representing comparisonresults and a first frequency differential signal representing afrequency difference. The third comparator is configured to comparephases and frequencies between one of the first signal and a secondsignal recorded beforehand on the optical disk and the frequency-dividedsignal of the write reference clock signal, and to output a third errorsignal representing comparison results and a second frequencydifferential signal representing a frequency difference. The selectioncircuit is configured to select any one of the first through third errorsignals output from the first through third comparators, respectively,and to exclusively output the signal selected. The control voltagegenerator is configured to generate a control voltage from the signaloutput from the selection circuit, and to output the control voltage.The voltage control oscillator is configured to generate and output thewrite reference clock signal having a frequency corresponding to thecontrol voltage input from the control voltage generator. The controlcircuit is configured to control operations of the selection circuitaccording to the first and second frequency differential signals.

[0006] The control circuit may be configured to cause the selectioncircuit to select and exclusively output the first error signal as thewrite reference clock signal during a predetermined time period t0 as aninitial action of a start-up operation of the apparatus.

[0007] The control circuit may be configured to cause the selectioncircuit to select and exclusively output the second error signal as thewrite reference clock signal after a lapse of the predetermined timeperiod t0.

[0008] The control circuit may be configured to cause the selectioncircuit to select and exclusively output the third error signal as thewrite reference clock signal when a difference in frequency indicated bythe first frequency differential signal output from the secondcomparator is smaller than or equal to a predetermined value α.

[0009] The control circuit may be configured to cause the selectioncircuit to select and exclusively output the second error signal as thewrite reference clock signal when a difference in frequency indicated bythe second frequency differential signal output from the thirdcomparator is greater than or equal to a predetermined value β which issmaller than the value α.

[0010] The control circuit may be configured to detect tracking statusduring the recording process on the optical disk, and when anoff-tracking is detected after a lapse of the predetermined time periodt0 from the start-up operation, the control circuit causes the selectioncircuit to stop outputting the first, second, or third error signalduring a predetermined time period t1.

[0011] The control circuit may be configured to cause the selectioncircuit to select and exclusively output the first error signal as thewrite reference clock signal after a lapse of the predetermined timeperiod t1.

[0012] The control circuit may be configured to cause the selectioncircuit to select and exclusively output the second error signal whentracking is established within the predetermined time period t1.

[0013] The first signal may be a wobble signal.

[0014] The second signal may be a land pre-pit signal.

[0015] The one of the first and second signals may be determinedaccording to a type of the optical disk.

[0016] This application further describes a novel method of recordinginformation on a recordable optical disk employing a constant angularvelocity recording method and generating a write reference clock signalused for obtaining recording timing in a data-recording operation on theoptical disk. In one example, a novel method includes the steps of firstcomparing, second comparing, third comparing, selecting, control voltagegenerating, write reference clock signal generating, and controlling.The first comparing step compares phases and frequencies between afrequency-divided signal of a predetermined reference clock signal inputfrom outside and a frequency-divided signal of the write reference clocksignal to output a first error signal representing comparison results.The second comparing step compares phases and frequencies between afirst signal recorded beforehand on the optical disk and thefrequency-divided signal of the write reference clock signal to output asecond error signal representing comparison results and a firstfrequency differential signal representing a frequency difference. Thethird comparing step compares phases and frequencies between one of thefirst signal and a second signal recorded beforehand on the optical diskand the frequency-divided signal of the write reference clock signal tooutput a third error signal representing comparison results and a secondfrequency differential signal representing a frequency difference. Theselecting step selects any one of the first through third error signalsoutput from the first through third comparing steps, respectively. Thecontrol voltage generating step generates a control voltage from thesignal selected in the selecting step. The write reference clock signalgenerating step generates the write reference clock signal having afrequency corresponding to the control voltage input in the controllingstep. The controlling step controls operations of the selecting stepaccording to the first and second frequency differential signals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] A more complete appreciation of the disclosure and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0018]FIG. 1 is a block diagram showing an outline structure of anoptical disk recording apparatus according to an exemplary embodiment;

[0019]FIG. 2 is a block diagram showing an exemplary structure of awrite clock generator of the optical recording apparatus shown in FIG.1; and

[0020]FIG. 3 is a flowchart showing an exemplary operation of a controlunit of the optical recording apparatus shown in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] In describing preferred embodiments illustrated in the drawings,specific terminology is employed for the sake of clarity. However, thedisclosure of this patent specification is not intended to be limited tothe specific terminology so selected and it is to be understood thateach specific element includes all technical equivalents that operate ina similar manner. Referring now to the drawings, wherein like referencenumerals designate identical or corresponding parts throughout theseveral views, particularly to FIG. 1, an optical disk recordingapparatus 1 according to an exemplary embodiment of the presentspecification is described. In FIG. 1, the optical disk recordingapparatus 1 includes a spindle motor 3, a motor drive 4, a servo circuit5, an optical pickup 6, a read amplifier 7, a first decoder 8, a seconddecoder 9, a D/A converter 10, a buffer manager 11, a buffer RAM 12, ahost interface 13, a third decoder 14, a write clock generator 15, afirst encoder 16, a second encoder 17, a laser control circuit 18, a CPU20, a ROM 21, and a RAM 22. The optical disk recording apparatus 1records data onto an optical disk 2 such as a CD-R/RW, a DVD+R/RW, and aDVD−R/RW. The optical disk 2 which contains data for audio and/or forpersonal computers, for example, is driven to spin by the spindle motor3. The spindle motor 3 spins under control by the motor driver 4 and theservo circuit 5.

[0022] The optical pickup 6 which reads and writes data on the opticaldisk 2 includes various components including a laser generator, anoptical system, a focus actuator, a track actuator, a light receivingelement, and a position sensor, which are not shown. The laser generatormay be a laser diode, for example. The optical pickup 6 irradiates alaser beam on the optical disk 2 to read data from or write data ontothe disk.

[0023] In a reading operation for reading out data from the optical disk2 (i.e., a data reproduction process), a reproduction signal read out bythe optical pickup 6 is amplified and is binarized by the read amplifier7. The first decoder 8 decodes the data amplified and binarized by theread amplifier 7 by carrying out an eight-to-fourteen modulation (EFM)demodulation and a CIRC (Cross Interleaved Read-solomon Code) operationsuch as a de-interleave or an error correction, for example, when theoptical disk has a CD format, or an eight-to-sixteen demodulation whenthe optical disk has a DVD format. The first decoder 8 outputs thedecoded data generated for audio or personal computer use to the seconddecoder 9. If the decoded data is generated for audio use, the D/Aconverter 10 performs digital-to-analog conversion on the data andoutputs a resultant audio signal.

[0024] The second decoder 9 stores the decoded data (e.g., audio orcomputer data) in the buffer RAM 12 through a buffer manager 11successively, and carries out an error correction in order to improvereliability on the data stored in the buffer RAM 12. In the errorcorrection, the second decoder 9 and the buffer RAM 12 exchange data,such as reading out data stored in the buffer RAM 12 and writing backdata into the buffer RAM 12, through the buffer manager 11.

[0025] After the error correction by the second decoder 9, the data isread out by the buffer manager 11 and transmitted through the hostinterface 13 to an outside host computer HC. The host interface 13 whichworks as an interface to the host computer HC conforms to standards suchas AT Attachment Packet Interface (ATAPI) or Small Computer SystemInterface (SCSI).

[0026] In a writing operation for writing data onto the optical disk 2(i.e., a data recording process), the optical pickup 6 reads out awobble signal and a land pre-pit signal from the optical disk 2. Thewobble signal is then input into the third decoder 14. The wobble signaltransmitted from the read amplifier 7 to the write clock generator 15 isreferred to as a wobble signal WOB, and the land pre-pit signal isreferred to as a land pre-pit signal LPP. The third decoder 14demodulates the input wobble signal to generate a synchronous signal,time information, and ID information and outputs the generatedinformation to the second encoder 17. The write clock generator 15receives a predetermined system clock signal CLK (FIG. 2) used as areference signal from outside. The write clock generator 15 alsoreceives from the read amplifier 7 the wobble signal WOB when theoptical disk 2 is a CD-R/RW or a DVD+R/RW, or the wobble signal WOB andthe land pre-pit signal LPP when the optical disk 2 is a DVD−R/RW.

[0027] The write clock generator 15 uses the input signals (i.e., thesystem clock signal CLK, the wobble signal WOB, and the land pre-pitsignal LPP) to generate a channel clock signal adequate to a datarecording speed on the optical disk 2. The channel clock signal isoutput to the second encoder 17. The second encoder 17 refers toinformation from the third decoder 14 to obtain an accurate startposition for writing onto the optical disk 2.

[0028] However, in a case like an additional recording in which data iswritten onto an area next to a preceding area where data is alreadyrecorded on the optical disk 2, quality of the wobble signal WOB may betoo low for the third decoder 14 to generate an accurate synchronoussignal, time information, and ID information. To avoid the problem, therecorded area on the optical disk 2 includes subcode data as well as asubcode synchronization for a synchronization signal in a case of a CDformat, for example. It is therefore possible to adjust a start positionfor recording by using the information such as the subcodesynchronization, subcode data, and ID information.

[0029] The data to be written onto the optical disk 2 is transmittedfrom the host computer HC to the buffer RAM 12 through the hostinterface 13 and the buffer manager 11. The first encoder 16 reads outthe data from the buffer RAM 12 through the buffer manager 11. The firstencoder 16 adds to the data an error correction code, an error detectionand correction (EDC) code, a SYNC code, header information, IDinformation, and so forth, and writes back data with the addedinformation to the buffer RAM 12.

[0030] The first encoder 16 reads out the prepared data from the bufferRAM 12 through the buffer manager 11 and, if the optical disk 2 has a CDformat, writes the data to a RAM (not shown) for a CIRC operation in thesecond encoder 17. If the optical disk 2 has a CD format, the secondencoder 17 carries out the CIRC operation on the data in the RAM for theCIRC operation by adding an error correction code and interleaving, andperforms the EFM modulation to output the resultant data. If the opticaldisk 2 has a DVD format, the second encoder 17 carries out theeight-to-sixteen modulation to output the resultant data. The dataoutput from the second encoder 17 is recorded onto the optical disk 2through the laser control circuit 18 and the optical pickup 6.

[0031] The CPU 20 controls operations of the first decoder 8, the seconddecoder 9, the host interface 13, the third decoder 14, the firstencoder 16, the second encoder 17, and so forth, using the ROM 21 andthe RAM 22. In data reproduction or data recording, the CPU 20 monitorscurrent status and issues various commands.

[0032] In FIG. 2, the write clock generator 15 forms a PLL circuit. Thewrite clock generator 15 includes a multiplication mode phase comparator31, an initial pull-in mode phase comparator 32, a write mode phasecomparator 33, a multiplexer 34, a charging pump circuit 35, a low passfilter (LPF) 36, a voltage controlled oscillator (VCO) 37, a controlcircuit 38, variable frequency dividers 40-42, and an FM componentremoval circuit 43. The write mode phase comparator 33 includes aCD-R/RW phase comparator 44, a DVD+R/RW phase comparator 45, and aDVD−R/RW phase comparator 46.

[0033] The multiplication mode phase comparator 31 compares phases andfrequencies between a frequency-divided signal S1 and afrequency-divided signal S2, and outputs the comparison results as anerror signal So1 to the multiplexer 34. Here, the frequency-dividedsignal S1 is obtained by a one-Nth frequency division on a predeterminedreference signal CLK, which is input from outside, by the variablefrequency divider 40. The frequency-divided signal S2 is obtained byone-Mth frequency division on a channel clock signal VCOCK, which isoutput from VCO 37, by the variable frequency divider 41. Frequency ofthe channel clock signal VCOCK is obtained by an expression Fr×M/N,where Fr represents frequency of the reference clock signal CLK. Eachdivision ratio of the variable frequency dividers 40 and 41 isdetermined according to the recording speed at which the optical diskrecording apparatus 1 writes data onto the optical disk 2.

[0034] The initial pull-in mode phase comparator 32 compares phases andfrequencies between the wobble signal WOB and a frequency-divided signalS3, and outputs the comparison results as an error signal So2 to themultiplexer 34. Here, the wobble signal WOB is detected from therecording medium on which recording is performed (i.e., the optical disk2), while the frequency-divided signal S3 is obtained by a frequencydivision on the channel clock signal VCOCK from the VCO 30 by thevariable frequency divider 42. The initial pull-in mode phase comparator32 also outputs a frequency differential signal Sf2, which shows adifference in frequencies between the wobble signal WOB and thefrequency-divided signal S3, to the control circuit 38. Division ratioof the variable frequency divider 42 is determined according to a typeof medium of the optical disk 2.

[0035] The write mode phase comparator 33 exclusively activates any oneof the CD-R/RW phase comparator 44, the DVD+R/RW phase comparator 45, orthe DVD−R/RW phase comparator 46, according to the selection signal Sc2being input from the control circuit 38. Consequently, the write modephase comparator 33 thus switches target signals and compares the phasesand frequencies of the target signals according to a type of medium ofthe optical disk 2, and outputs the comparison results as an errorsignal So3 to the multiplexer 34. The write mode phase comparator 33also outputs a difference of frequencies between the target signals as afrequency differential signal Sf3 to the control circuit 38.

[0036] Specifically, in a case of CD-R/RW where frequency of the wobblesignal WOB is modulated, the FM component removal circuit 43 removes afrequency modulation component from the wobble signal WOB to output asignal S4. The CD-R/RW phase comparator 44 then compares phases andfrequencies between the signal S4 and the frequency-divided signal S3,and outputs the comparison results as an error signal So3 to themultiplexer 34. Here, the frequency-divided signal S3 is obtained byfrequency division on the channel clock signal VCOCK from-the VCO 30 bythe variable frequency divider 42. The CD-R/RW phase comparator 44 alsogenerates a signal showing a difference in frequencies between thesignal S4 and the frequency-divided signal S3, and output the generatedsignal to the control circuit 38 as a frequency differential signal Sf3.

[0037] The DVD+R/RW phase comparator 45 compares phases and frequenciesbetween the wobble signal WOB and the frequency-divided signal S3, andoutputs the comparison results as an error signal So3 to the multiplexer34. The DVD+R/RW phase comparator 45 also generates a signal showing adifference in frequencies between the wobble signal WOB and thefrequency-divided signal S3, and output the generated signal as afrequency differential signal Sf3 to the control circuit 38. TheDVD−R/RW phase comparator 46 compares phases and frequencies between theland pre-pit signal LPP and the frequency-divided signal S3, and outputsthe comparison results as an error signal So3 to the multiplexer 34. TheDVD−R/RW phase comparator 46 also generates a signal showing adifference in frequencies between the land pre-pit signal LPP and thefrequency-divided signal S3, and outputs the generated signal to thecontrol circuit 38 as a frequency differential signal Sf3.

[0038] The multiplexer 34 selects one signal among input error signalsSo1 through So3 according to a type of medium of the optical disk 2 forrecording and to the control signal input from the control circuit 38.The selected signal is exclusively output to the charging pump circuit35. A signal output from the charging pump circuit 35 is smoothed and isoutput to the VCO 37 as a control voltage. The VCO 37 generates achannel clock signal VCOCK according to the input control voltage, andoutputs a voltage which is used as a channel clock signal to control thewriting operation over the optical disk 2. Besides, the channel clocksignal used for the writing control over the optical disk 2 may beobtained by a frequency division on the signal VCOCK output from the VCO37 with the variable frequency dividers. The control circuit 38 is ableto cause the multiplexer 34 to stop outputting a signal by using thecontrol signal Sc1, in some cases described below.

[0039] The control circuit 38 receives from the CPU 20 in FIG. 1 aCAV/CLV selection signal Ss1, a medium specification signal Sm, atracking signal St, an error signal Se, and a reset signal Sr. TheCAV/CLV selection signal Ss1 represents which method between CAV and CLVis used for recording onto the optical disk 2. The medium specificationsignal Sm specifies a type of medium of the optical disk 2. The trackingsignal St indicates whether or not tracking is successfully carried out.The error signal Se represents a predetermined error signal. The resetsignal Sr indicates execution of a predetermined reset operation. Thecontrol circuit 38 generates and outputs the control signal Sc1 to themultiplexer 34, by referring to the CAV/CLV selection signal Ss1, thetracking signal St, and the error signal Se. The control circuit 38 alsooutputs the selection signal Sc2 corresponding to the mediumspecification signal Sm to the write mode phase comparator 33. Thetracking signal St and the error signal. Se may be output from the servocircuit 5 to the control circuit 38.

[0040]FIG. 3 is a flowchart showing an example recording operation ofthe control circuit 38 according to the above-described configuration.By referring to FIG. 3, the operation of the control circuit 38 will bedescribed in detail.

[0041] In Step S01, the reset signal Sr is asserted from the CPU 20, thecontrol circuit 38 enters a multiplication mode as an initial statecausing multiplexer 34 to exclusively output the error signal So1 fromthe multiplication mode phase comparator 31 to the charging pump circuit35. The multiplication mode is provided in cases of a recording processof the CLV method requiring a channel clock signal with constantfrequency and a recording process of the CAV method to prevent the PLLbeing unstable when the wobble signal WOB or the land pre-pit signal LPPbecomes inaccurate due to the initial pull-in, an off-track error, anoff-servo error, and so forth.

[0042] In Step S02, in the CAV recording method, the control circuit 38then checks whether or not a predetermined time t0 has passed andtracking is successfully carried out. The time t0 is to a locktime ofthe PLL in the multiplication mode. When the time t0 has passed and thetracking is successfully carried out, the result of Step S02 is YES andthe process proceeds to Step S03. In Step S03, the control circuit 38enters an initial pull-in mode causing the multiplexer 34 to exclusivelyoutput the error signal So2 from the initial pull-in mode phasecomparator 32 to the charging pump circuit 35. In the initial pull-inmode, the VCO 37 outputs a signal VCOCK in synchronization with thewobble signal WOB detected from the optical disk 2. The signal clockVCOCK is referred to as a channel clock signal required for therecording process. When the time t0 has not passed or the time t0 haspassed but the tracking is not successfully carried out, the result ofStep S03 is NO and the process returns to the Step S01.

[0043] Then, in Step S04, the control circuit 38 in the initial pull-inmode checks whether or not the tracking is successfully carried out.When tracking is successfully carried out, the result of Step S04 is YESand the process proceeds to Step S05. In Step S05, the control circuit38 detects the frequency differential signal Sf2 input from the initialpull-in mode phase comparator 32 to check whether or not the differenceindicated by the frequency differential signal Sf2 is smaller than orequal to a predetermined setting value α. The setting value α indicatinga frequency range is determined in consideration of a capture range anda pull-in speed of the write mode. In Step S05, when the difference infrequencies is greater than the setting value α, the result of Step S05is NO and the process returns to Step S03. If the difference infrequencies is smaller than or equal to the setting value α, the resultof Step S05 is YES and the process proceeds to Step S06. In Step S06,the control circuit 38 enters a write mode causing the multiplexer 34 toexclusively output the error signal So3 from the write mode phasecomparator 33 to the charging pump circuit 35.

[0044] In the write mode, the write mode phase comparator 33 comparesphases and frequencies between one of the wobble signal WOB and the landpre-pit signal LPP detected from the optical disk 2 and thefrequency-divided signal So3, and generates the error signal So3. Theerror signal So3 is output through the multiplexer 34, the charging pumpcircuit 35, and the LPF 36 to the VCO 37 where the signal VCOCK isgenerated. In the write mode, the signal VCOCK in synchronization withthe wobble signal WOB or the land pre-pit signal LPP detected from theoptical disk 2 is generated. A channel clock signal required for therecording process on the optical disk 2 is thus obtained. In contrast tothe initial pull-in mode in which the channel clock signal is generatedby pulling in frequencies to some degree, in the write mode, the channelclock signal for writing data onto the optical disk 2 is generated bypulling in phases and frequencies with more accuracy.

[0045] Then, in Step S07, the control circuit 38 in the write modechecks whether or not the tracking is successfully carried out. Whentracking is successfully carried out, the result of Step S07 is YES andthe process proceeds to Step S08. In Step S08, the control circuit 38detects the frequency differential signal Sf3 input from the initialpull-in mode phase comparator 33 to check whether or not the differenceindicated by the frequency differential signal Sf3 is greater than orequal to a predetermined setting value β which is smaller than thesetting value α, and whether or not any error is detected such as aspindle error, a servo error including an off-track error, or any otherabnormal conditions during the writing process.

[0046] The setting value β is set to a value of frequency variationwhich is allowed in the writing process to assure the writing quality.When the difference in frequencies is determined as being greater thanor equal to the predetermined setting value β or when any of the errorsis detected in Step S08, the result of Step S08 is YES and the processreturns to Step S03. When the difference in frequencies is determined asgreater than or equal to the predetermined setting value β and/or whennone of the errors is detected, the result of Step S08 is NO and theprocess returns to Step S06.

[0047] In the meanwhile, when tracking is determined as not successfullycarried out in Step S04 or Step S07, the result of Step S04 or Step S07is NO and the process proceeds to Step S09. In Step S09, the controlcircuit 38 enters a hold mode causing the multiplexer 34 to stopoutputting a signal to the charging pump circuit 35. The hold mode isprovided in order to maintain the PLL frequency, i.e., the frequency ofthe signal VCOCK. During the hold mode, the multiplexer 34 stopsoutputting one of the error signals to the charging pump circuit 35.

[0048] Then, in Step S10, the control circuit 38 in the hold mode checkswhether or not a predetermined time t1 has passed. When the time t1 hasnot passed, the result of Step S10 is NO and the process returns to StepS09. When the time t1 has passed, the result of Step S10 is YES and theprocess returns to Step S01. The time t1 may be set to such a timeperiod in which the PLL can hold the current frequency. This is toincrease the pull-in speed of the PLL by pulling in the frequencypreviously used in a case of a short track jump, for example, in whichthe channel clock signal required for a next writing process does notvary much in frequency.

[0049] An ideal transition order of a state from initial toready-to-write onto the optical disk 2 is the multiplication mode ofStep S01, the initial pull-in mode of Step S03, and the write mode ofStep S06. In a basic operation, when the tracking is successfullycarried out, the wobble signal WOB or the land pre-pit signal LPP isdetected so that the process enters the write mode. On the contrary, ina case of an off-track error in a seek operation or the like whereneither the wobble signal WOB nor the land pre-pit signal LPP can bedetected, the process enters the multiplication mode in order to preventthe PLL from being unstable. However, in a case of a short track jump orthe like in which a time period of an off-track error is rather short,the process preferably enters the hold mode in which fluctuations of thePLL frequency are restrained.

[0050] The transition process shown in FIG. 3 is controlled with thecontrol circuit 38. As an alternative, some part can be set manually.When the process is manually set to the initial pull-in mode, and thesuccessive process is set as automatic, for example, the process startsat the initial pull-in mode of Step S03 in FIG. 3.

[0051] As described above, in the optical disk recording apparatusaccording to the embodiment of the present specification, the controlcircuit 38 automatically switches among the error signal So1 from themultiplication mode phase comparator 31, the error signal So2 from theinitial pull-in mode phase comparator 32, and the error signal So3 fromthe write mode phase comparator 33 output signal to the charging pumpcircuit 35, according to a state of the wobble signal WOB or the landpre-pit signal LPP. It is therefore possible to reduce settling timerequired for obtaining a stable channel clock signal from the wobblesignal or land pre-pit signal detected from the optical disk 2.Consequently, the optical disk recording apparatus 1 can generate thechannel clock signal with more accuracy and stability.

[0052] Numerous additional modifications and variations are possible inlight of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims, the disclosure of this patentspecification may be practiced otherwise than as specifically describedherein.

[0053] This patent specification is based on Japanese patentapplication, No. JPAP2002-345918 filed on Nov. 28, 2002 in the JapanesePatent Office, the entire contents of which are incorporated byreference herein.

What is claimed is:
 1. An optical disk recording apparatus which recordsinformation on a recordable optical disk employing a constant angularvelocity recording method and generates a write reference clock signalused for obtaining recording timing in a data-recording operation on theoptical disk, the apparatus comprising: a first comparator configured tocompare phases and frequencies between a frequency-divided signal of apredetermined reference clock signal input from outside and afrequency-divided signal of the write reference clock signal, and tooutput a first error signal representing comparison results; a secondcomparator configured to compare phases and frequencies between a firstsignal recorded beforehand on the optical disk and the frequency-dividedsignal of the write reference clock signal, and to output a second errorsignal representing comparison results and a first frequencydifferential signal representing a frequency difference; a thirdcomparator configured to compare phases and frequencies between one ofthe first signal and a second signal recorded beforehand on the opticaldisk and the frequency-divided signal of the write reference clocksignal, and to output a third error signal representing comparisonresults and a second frequency differential signal representing afrequency difference; a selection circuit configured to select any oneof the first through third error signals output from the first throughthird comparators, respectively, and to exclusively output the signalselected; a control voltage generator configured to generate a controlvoltage from the signal output from the selection circuit, and to outputthe control voltage; a voltage control oscillator configured to generateand output the write reference clock signal having a frequencycorresponding to the control voltage input from the control voltagegenerator; and a control circuit configured to control operations of theselection circuit according to the first and second frequencydifferential signals.
 2. The apparatus according to claim 1, whereinsaid control circuit causes said selection circuit to select andexclusively output said first error signal as the write reference clocksignal during a predetermined time period t0 as an initial action of astart-up operation of the apparatus.
 3. The apparatus according to claim2, wherein said control circuit causes said selection circuit to selectand exclusively output said second error signal as the write referenceclock signal after a lapse of the predetermined time period t0.
 4. Theapparatus according to claim 1, wherein said control circuit causes saidselection circuit to select and exclusively output said third errorsignal as the write reference clock signal when a difference infrequency indicated by the first frequency differential signal outputfrom said second comparator is smaller than or equal to a predeterminedvalue α.
 5. The apparatus according to claim 4, wherein said controlcircuit causes said selection circuit to select and exclusively outputsaid second error signal as the write reference clock signal when adifference in frequency indicated by the second frequency differentialsignal output from said third comparator is greater than or equal to apredetermined value β which is smaller than said value α.
 6. Theapparatus according to claim 2, wherein said control circuit detectstracking status during the recording process on the optical disk, andwhen an off-tracking is detected after a lapse of the predetermined timeperiod t0 from the start-up operation, said control circuit causes saidselection circuit to stop outputting the first, second, or third errorsignal during a predetermined time period t1.
 7. The apparatus accordingto claim 6, wherein said control circuit causes said selection circuitto select and exclusively output the first error signal as the writereference clock signal after a lapse of said predetermined time periodt1.
 8. The apparatus according to claim 6, wherein said control circuitcauses said selection circuit to select and exclusively output saidsecond-error signal when tracking is established within saidpredetermined time period t1.
 9. The apparatus according to claim 1,wherein the first signal is a wobble signal.
 10. The apparatus accordingto claim 1, wherein the second signal is a land pre-pit signal.
 11. Theapparatus according to claim 1, wherein the one of the first and secondsignals is determined according to a type of the optical disk.
 12. Anoptical disk recording apparatus which records information on arecordable optical disk employing constant angular velocity recordingmethod and generates a write reference clock signal used for obtainingrecording timing in a data-recording operation on the optical disk, theapparatus comprising: first comparing means for comparing phases andfrequencies between a frequency-divided signal of a predeterminedreference clock signal input from outside and a frequency-divided signalof the write reference clock signal, and for outputting a first errorsignal representing comparison results; second comparing means forcomparing phases and frequencies between a first signal recordedbeforehand on the optical disk and the frequency-divided signal of thewrite reference clock signal, and for outputting a second error signalrepresenting comparison results and a first frequency differentialsignal representing a frequency difference; third comparing means forcomparing phases and frequencies between one of the first signal and asecond signal recorded beforehand on the optical disk and thefrequency-divided signal of the write reference clock signal, and foroutputting a third error signal representing comparison results and asecond frequency differential signal representing a frequencydifference; selection means for selecting any one of the first throughthird error signals output from the first through third comparing means,respectively, and for exclusively outputting the signal selected;control voltage generating means for generating a control voltage fromthe signal output from the selecting means, and for outputting thecontrol voltage; voltage control oscillating means for generating andoutputting the write reference clock signal having a frequencycorresponding to the control voltage input from the control voltagegenerating means; and control means for controlling operations of theselecting means according to the first and second frequency differentialsignals.
 13. The apparatus according to claim 12, wherein said controlmeans causes said selection means to select and exclusively output saidfirst error signal as the write reference clock signal during apredetermined time period t0 as an initial action of a start-upoperation of the apparatus.
 14. The apparatus according to claim 13,wherein said control means causes said selection means to select andexclusively output said second error signal as the write reference clocksignal after a lapse of the predetermined time period t0.
 15. Theapparatus according to claim 12, wherein said control means causes saidselection means to select and exclusively output said third error signalas the write reference clock signal when a difference in frequencyindicated by the first frequency differential signal output from saidsecond comparing means is smaller than or equal to a predetermined valueα.
 16. The apparatus according to claim 15, wherein said control meanscauses said selection means to select and exclusively output said seconderror signal as the write reference clock signal when a difference infrequency indicated by the second frequency differential signal outputfrom said third comparing means is greater than or equal to apredetermined value β which is smaller than said value α.
 17. Theapparatus according to claim 13, wherein said control means detectstracking status during the recording process on the optical disk, andwhen an off-tracking is detected after a lapse of the predetermined timeperiod t0 from the start-up operation, said control means causes saidselection means to stop outputting the first, second, or third errorsignal during a predetermined time period t1.
 18. The apparatusaccording to claim 17, wherein said control means causes said selectionmeans to select and exclusively output the first error signal as thewrite reference clock signal after a lapse of said predetermined timeperiod t1.
 19. The apparatus according to claim 17, wherein said controlmeans causes said selection means to select and exclusively output saidsecond error signal when tracking is established within saidpredetermined time period t1.
 20. The apparatus according to claim 12,wherein the first signal is a wobble signal.
 21. The apparatus accordingto claim 12, wherein the second signal is a land pre-pit signal.
 22. Theapparatus according to claim 12, wherein the one of the first and secondsignals is determined according to a type of the optical disk.
 23. Amethod of recording information on a recordable optical disk employing aconstant angular velocity recording method and generating a writereference clock signal used for obtaining recording timing in adata-recording operation on the optical disk, the method comprising thesteps of: first comparing phases and frequencies between afrequency-divided signal of a predetermined reference clock signal inputfrom outside and a frequency-divided signal of the write reference clocksignal to output a first error signal representing comparison results;second comparing phases and frequencies between a first signal recordedbeforehand on the optical disk and the frequency-divided signal of thewrite reference clock signal to output a second error signalrepresenting comparison results and a first frequency differentialsignal representing a frequency difference; third comparing phases andfrequencies between one of the first signal and a second signal recordedbeforehand on the optical disk and the frequency-divided signal of thewrite reference clock signal to output a third error signal representingcomparison results and a second frequency differential signalrepresenting a frequency difference; selecting any one of the firstthrough third error signals output from the first through thirdcomparing steps, respectively; generating a control voltage from thesignal selected in the selecting step; generating the write referenceclock signal having a frequency corresponding to the control voltageinput in the controlling step; and controlling operations of theselecting step according to the first and second frequency differentialsignals.
 24. The method according to claim 23, wherein said controllingstep causes said selecting step to select and exclusively output saidfirst error signal as the write reference clock signal during apredetermined time period t0 as an initial action of a start-upoperation of the method.
 25. The method according to claim 24, whereinsaid controlling step causes said selecting step to select andexclusively output said second error signal as the write reference clocksignal after a lapse of the predetermined time period t0.
 26. The methodaccording to claim 23, wherein said controlling step causes saidselecting step to select and exclusively output said third error signalas the write reference clock signal when a difference in frequencyindicated by the first frequency differential signal output from saidsecond comparing step is smaller than or equal to a predetermined valueα.
 27. The method according to claim 26, wherein said controlling stepcauses said selecting step to select and exclusively output said seconderror signal as the write reference clock signal when a difference infrequency indicated by the second frequency differential signal outputfrom said third comparing step is greater than or equal to apredetermined value β which is smaller than said value α.
 28. The methodaccording to claim 24, wherein said controlling step detects trackingstatus during the recording process on the optical disk, and when anoff-tracking is detected after a lapse of the predetermined time periodto from the start-up operation, said controlling step causes saidselecting step to stop outputting the first, second, or third errorsignal during a predetermined time period t1.
 29. The method accordingto claim 28, wherein said controlling step causes said selecting step toselect and exclusively output the first error signal as the writereference clock signal after a lapse of said predetermined time periodt1.
 30. The method according to claim 29, wherein said controlling stepcauses said selecting step to select and exclusively output said seconderror signal when tracking is established within said predetermined timeperiod t1.
 31. The method according to claim 23, wherein the firstsignal is a wobble signal.
 32. The method according to claim 23, whereinthe second signal is a land pre-pit signal.
 33. The method according toclaim 23, wherein the one of the first and second signals is determinedaccording to a type of the optical disk.